In most large airplanes, it is standard for floor beams to run in a lateral direction, except in the wing box section where the floor beams run in a forward and aft direction. As a result, the floor beams over the wing box flex (i.e., expand and contract laterally) with movement of the wings. While this flexing may occur at any stage of the airplane's flight, it is most pronounced as the wings bounce up and down during taxiing, especially at high gross weights. With airplanes that carry fuel in their wings, the wings have an even lower resting position and the resulting wing bounce exerts even greater flexing to the floor beams than is found in airplanes not carrying fuel in this manner.
In cargo airplanes, loaded cargo containers and pallets normally sit two abreast across the width of the airplane, each container or pallet being vertically restrained to the main cargo deck on the inside by centerline restraints and on the outboard side by vertical restraints and side locks. Horizontal restraint is provided by end locks placed forward and aft of the containers or pallets, and/or by the side locks in the case of containers.
Current centerline restraints have a pair of vertically extending inside heads and a pair of vertically extending outside heads, each head having a horizontally extending toggle that extends outboard to engage a receptacle in the container or the top of the pallet, thereby providing vertical restraint. The toggle of each head is spring loaded such that it may be rotated out of engagement during the loading of the cargo. The inside heads typically used in current centerline restraints are disclosed in U.S. Pat. No. 3,906,870, issued to Alberti on Sept. 23, 1975. As shown, these inside heads are manually retractable and are designed to engage full-width containers and pallets (e.g., 96 inches on the Boeing 747 cargo airplane). While not disclosed in the Alberti patent, the outside heads of current centerline restraints are automatically retractable upon engagement by a container or pallet and are designed to vertically restrain containers and pallets of reduced width (e.g., 88 inches on the Boeing 747 cargo airplane).
In order for the cargo containers and pallets to be loaded, the distance from the centerline restraints to the outboard vertical restraints and side locks must be slightly greater than the width of the container or pallet. If not, there would not be the clearance required to move the cargo into position. Additionally, it is quite common for containers and pallets to be slightly undersized because the manufacturers do not closely follow the dimensional specifications set for the containers and pallets.
Consequently, the combination of a slight amount of clearance, an undersized container or pallet, and flexing of the floor beam may lead to the toggles of current centerline restraints being pulled out of engagement with the container or pallet over the wing box section of the airplane. If the vertical restraints and side locks on the outboard side are similarly pulled out of engagement, the container or pallet is no longer vertically restrained. When this occurs with large containers, which are not capable of being end locked, the container may become totally unrestrained and thereby lead to catastrophic events.
While loaded containers and pallets normally sit two abreast in cargo airplanes, extremely heavy loads must straddle the centerline of the airplane, usually over the wing box section. This positioning ensures that the load is balanced during flight both in a forward and aft direction and in a lateral direction. If not so positioned, the airplane's fuel efficiency is drastically cut and the safety of the flight is greatly diminished due to handling difficulties. Before a load can be positioned in this manner, it is necessary that the inside heads of current centerline restraints be manually retracted. Because centerline restraints are located at short intervals down the centerline of the wing box section, manual retraction of the heads is both tedious and time consuming.
As a result, there has been a long-felt need for a centerline restraint for vertically restraining cargo containers and pallets over the wing box section of cargo airplanes that maintains contact with the container or pallet during periods of extreme floor beam flexing, that is automatically retractable when a load must be positioned straddling the centerline of the airplane, and that attaches to existing mounts. This invention is directed to satisfying this need.